In hopes of obtaining a better understanding of the relationship between the steroidogenesis and the action of ACTH in adrenal cortex, we have been studying the molecular basis of the enzyme, proteins and other factors involved in adrenal cortex. In extending this study, I propose works on (1) chemical and physical properties of adrenodoxin, (2) mechanism of hydroxylation, (3) biosynthesis of adrenodoxin, (4) aging processes of adrenal, testis and ovary mitochondria, (5) purification and properties of cytochrome P-450 and (6) other related subjects.